Furnace control



Jan. 14, D B ET AL I FURNACE CONTROL Filed July 15. 1925 2 Sheets-Sheet l INVENTOR Pascae D. Bea/1 ATTORNEY Jan. 14, 1930. BEAN ET AL FURNACE CONTROL Filed July 15, 1925 2 Sheets-Sheet Patented Jan. 14, 1930 UNITED ST P TENT OFFIC ROSCOE BEAN AND FREDERICK W. SIDE, OF PHILADELPHIA, PENNSYLVANIA,

ASSIGNORS TO THE BROWN INSTRUMENT COMPANY, OF PHILADELPHIA, PENN- SYLVANIA, A CORPORATION OF PENNSYLVANIA FURNACE CONTROL One primary object of the present invention is to provide an improved mechanism for, and method of controlling electric furnaces. More specifically, the object of 5 the invention is to provide an improved an electric furnace, and the invention is characterized bythe manner in, and provisions by which heating current is normally supplied to the furnace as required to ma ntam a desired temperature condition therein, and the supply of current to the furnace is reduced when necessary to avoid overheating'the resistor or heating means of the furnace, even though the furnace temperature proper is then not as high as may be desirable. Further objects of the invention are to provide improvements in control mechanism primarily devised and adapted for use in an electric furnace control system of the type referred but also adapted for use in control instruments employed for other purposes.

The various features of novelty characterizing our invention are pointed out with particularity in the claims annexed to and forming a part of the present specification; but for a better understanding of the invention, its advantages and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described a preferred embodiment of our invention.

Of the drawings:

Fig. 1 is a front elevation of a control instrument; r

Fig. 2 is a plan view, with parts broken away and in section, of the control instrument shown in Fig. 1;

Fig. 3 is a section on the line 3-3 of Fig. 1;

Fig. 4 is an elevation of a ortion of the mechanism shown in elevation in Fig. 3, with parts in different relative positions;

Fig. 5 is an elevation of another portion of the control instrument; and

Fig. dis a diagram illustrating our im proved electric control system.

The control instrument A, shown in the drawings, comprises a millivoltmeter or gal- 1925. Serial No. 43,764.

vanometer B, sufiieiently sensitive to respond to the current flow created h an ordinary thermo-couple of the type use for pyrometric work. B represents the swinging ointor of the galvanometer and in Fig. 6, represents the winding or movable coil of the galvanometer. The free end of the pointer 13 is intermittently depressed to actuate control contacts as hereinafter explained, by a depressor mechanism comprising a yoke shaped depressor C proper which is pivotally supported by means of pivot screws C carrie by posts A forming a part of the instrument frame-work. Advantageously, and as shown, the depressor G moves down to depress the free end of the pointer B under the action of gravity when free to do so, but is normally held up out of contact with the ointer by a vertically movable member D aving a neck )ortion D which is straddled by a bifurcated ortion C of the depressor. The member is intermittently raised to permit the depressor C to engage and depress the pointer B, and is then pulled down to move the depressor out of engagement with the pointer by mechanism comprising a motor F which may be, and as shown is, a so-called \Varren electric clock. The motor F comprises a slow speed shaft F making one rotation in a minute or so, and carrying a depressor actuating cam E. The latter is provided with two diametrically opposed notches J for actuating the depressor twice in each revolution of the shaft F. The provisions through which the rotating cam E gives vertical movement to the member D, com rises a part d pivotally connected atd to the ower end of the member D proper, to swing toward and away from the cam. The part (Z is formed with a tooth d. The extent to which the part d can move awa from the cam E is controlled by a guide carried by the instrument frame-work. For the major portion of each half revolution, the peri heral edge of the cam E, which rotates in the direction of the arrow shown in Fig. 4, bears a ainst the upper side of the tooth d and hol the member D in its lowermost position in which the depressor C is held above the pointer. A slight rotation of the cam E from the posi- I begins to tion shown in Fig. 4, permits the point of the tooth d to move past the lower edge of the adjacentnotch E and the depressor'C is then free to fall and depress the pointer. As the depressor descends, the member D is lifted into the position shown in Fig. 3. As the cam notch E, so that the continued rotative.

movement of the cam E almost immediately ull the member d down and in a few seconc s raises the depressor C out of enga ement with the pointer B.

11 each pointer depressing movement of the depressor C, the latter causes one or another, dependent on the position of the pointer B, of three spring contacts h, i, and j to be depressed into engagement with the corresponding contacts h, 1", and j, respectively. The contacts h and i are depressed by the depressor C through the pointer B whenever the latter is above either of those contacts at the time the pointer is depressed. When the pointer B is depressed at a time when the pointer is not above either of the contacts h or 2', a contact actuator in the form of screw C adjustably mounted in the depressor C, engages the contact j, and moves it against the contact j. \Vhen the pointer is above either of the contacts h or 2', the

downward movement of the depressor C is arrested before the actuator C engages the contact j and moves the latter'into engage ment with the contact :5. The contacts h and It are mounted on a table H carried by the free end of an arm H pivoted to the instrument frame-work at A and the contacts 2' and z" are mounted on a table I carried by arm I also pivoted on the pin A Atits rear end the arm H is provided with a gear segment H coaxial with the pivot pin A and having its teeth in mesh with a spur gear K. The latter, as shown. is in mesh with a spur gear K provided with a coupling jaw K adapted to engage a co-operating coupling jaw K carried at the lower end of a rotatable adjustor K mounted in the meter frame-work and provided at its upper end with means by which it may be rotated, as by having its head K formed with a slot for engagement by a screw driver or like implement. A spring K normally holds the member K in its elevated position in which the clutch member K is separated from the clutch member K When the member K is depressed to couple the clutch jaws K and K a collar or shoulder K, formed on the member K, engages an arm portion C of the depressor C and positively holds the latter in the position in which it clears the pointer B. This avoids all possibility of injury to the pointer while the arm H or the arm I is being adjusted.

, The rotation of the gear K angularly adjuststhe arm H about the pivotal axis A", and thereby changes the temperature indication of the pointer B at which the latter will be above the contact It. The adjustment of the. arm H is also employed to adjust the arm I through a connection between the arms/H and 1 comprising a pin H carried by the arm H and working in an elongated slot I formed in an extension I of the arm I. The play of the pin H in the slot I is sufficient to permit all proper relative adjustments of the contacts h and 2'. By adjusting the arm H to bring the pin H into engagement with one end or the other of the slot 1 and then continuing the adjustment of the arm H, the arm I may be set in any desired angular position after which the rotation of the gear K may be reversed to move the contact h as much closer to the contact arrangementbein such that when the cam F engages the guide L it quickly shifts the member L about the pivot A in a clockwise direction, as seen in Fig. 6, and thus cause the contact conductors m and m of a switch or commutator M carried by the member L, to respectively engage spring contacts Q, and Q. WVhen the continuing rotation of the cam F causes the cam F to engage the guide portion L of the member L, the latter is quickly shifted in the opposite direction and the contact conductors m and m are .then brought into engagement with spring contacts P and P,-"respectively. The member .L may be frictionally held in whichever posi- I tion it is shifted into. As shown, a guide pin A projects through a slot formed in the member L. The contact conductors m and m mayconsistotsectionsofplatinumwire. The member L is also provided with an arm L which engages a contact member 0 and moves the latter out of engagement with a contact 0 whenever the member is moved into-the position in which the conductors m and m engage the spring contacts Q and Q, respectively. The contact member 0 is pivotally connected to the instrument framework at A and a spring 0 tends to hold ]the rggmber O in engagement with the mem- In Fig. 6 we have diagrammatically illustrated the use of the control instrument shown in Figs. 1 and 5 in a control system for an electric furnace S of which R represents a heating resistor. Associated with the resistor R and responsive to the temperature thereof is a t-hermo-couple T, while a second thermo-couple T is responsive to the temperature in the heating chamber S of the furnace S. The resistor R receives current from supply conductors 1 and 2, one terminal of the resistor B being directly connected by a conductor 3 to the supply conductor 1, while the other terminal of the resistor is connected to the supply conductor 2, ordisconnected therefrom, by means of a regulating switchU and conductor 4 running from the resistor terminal to the switch U, and a conductor 4 running from the switch contact U to the supply conductor 2. The regulating switch U is moved toward and away from the contact U to close and open the resistor energizing circuit by the control instrument A in response to the temperature conditions to which the thermo-. couples T and T are subjected as hereinafter explained. In the known form of regulating switch mechanism shown, the switch member U is in the form of a pivoted'armaturewhich is moved into engagement with the switch contact U when the electromagnet U is energi'zed. When the magnet U is de-ener-.-

gized, the switch member U is moved by gravity into the position shown in Fig. 6 in which the resistor circuit is open between the switch member U and the contact member U. I With the switch U in the open position shown in Fig. 6, the energization of the magnet U with the consequent movement of the switch U into its closed position, is brought about whenever the control instrument A connects the conductor 13 to the supply conductor 1, in a manner hereinafter explained. The magnet energizing circuit then closed, includes the conductor 1, conductor 13, winding of the electromagnet U conductor 134, conductor 4, and supply conductor 2. After the switch U has thus been closed, the subsequent disconnection of the conductor 13 from the supply conductor 1 does not open the switch U, since thecurg'ent then flowing through the windingof, the magnet U through the circuit including the conductors 2, 4, and 134, winding of the magnet U and a resistor U connecting the winding U to the supply conductor 1, sufliciently energizes the magnet to tor 2, the magnet U is short-circuited and deenergized as both terminals of the magnet winding are then also connected to the supply The commutator contact wire m is connected 'to one term nal of the movable galvanometer winding 6, and the second terminal of the latter is connected by the conductor 12to the commutator contact wire m. The control conductor 13 is connected to thei-nstrument contact 2', and also to the instrument contact 0. The instrument contacts 0, h, and j are connected to one another by a conductor 14. The instrument contacts h and i are connected to the supply conductor 2 by a conductor 15. The instrument contact 7' is connected to the supply conductor 1 by a conductor 16. The mstrument motor F is energized from the supply conductors 1 and 2 through conductors 5, 15, 6 and 16. As shown, some of the heat required by the furnace S may be furnished by a resistor R, not subject to the control of the instrument A, but adapted to be operatlvely connected to, and disconnected from the supply conductors 1 and 2 by a manually actuated switch R In the operation of the control apparatus shown in the drawing, motor F operates through the cam E, part d, and member D to permit the depressor C to swing down and depress the galvanometer pointer B at regular intervals of 30 seconds or so, and within a short period of some 5 or 10 seconds after each engagement of the pointer by the depressor C, the latter is lifted by the action of the cam E on the part 03 sufficiently to release the pointer. After each depression of the pointer B, the member L is shifted from one limit to the other of its range of movement so that during each alternate depression of the pointer B, the galvanometer winding 1) s connected to the thermo-couple T and durmg the intervening depressions of the pointer B, the winding 6 is connected to the thermocouple T. The temperature of the resistor R Wlll normally be substantially higher, frequently by some hundreds of degrees, than the temperature in the furnace chamber S. In consequence, the instrument pointer B will normally indicate a higher temperature when the meter winding b connected to the thermo-couple T than when it is connected to the thermo-couple T. In the instrument shown, the free end of the pointer B swings to the right, as seen in Fig. 1, to indicate higher temperatures, and swings to the left tact j and moves the. latter through the contacts 2" and z, and conductortact h, and the downward movement of the depressor C will continue until the contact actuator C carried by it engages the coninto engagement with the contact 7''. This fully energizes the magnet U by connecting the conductor 13 to the supply conductor 1, through circuit connections including-conductor 16, contact 7'', contact 7', conductor 14, and the contacts 0 and O, which are closed in the corresponding position ofthe member L. The energization of the magnet U moves the switch member U into its closed position if it previously was in its open position. If the temperature of the thermdcouple' Tis high enough when connected to the meter winding 6 to hold the meter pointer B above the contact h, the contact h is moved into engagement with the contact h when the depressor C depresses the pointer. This connects the conductor 13 through contacts 0 and O, conductor 14, contact h, contact 72., and conductor'lt') to the supply conductor 2, and thereby, as previously explained, short circuits the magnet U, with the result that the switch U if previousy closed then opens. If the temperature of the thermo-couple T is high enough, when that thermo-couple is connectedto the meter winding 6, to move the ointer b above the contact 27, the descent o the depressor C then causes the contact 2 to engage the contact z" and thereby de-energizes the magnet U and opens the switch member U, if the latter Were previously closed, by connecting the supply conductor 13 to the supply conductor 2 through the contacts 2" and 'z', and conductor 15.

When the member L is shifted into the position in which the contact conductors m and m. of the switch M connect the resistor temperature measuring thermo-couple T to the terminals of the meter winding 6, and in Which the switch arm M holds the contact 0 out of engagement with the contact 0, the depression of the pointer B affects the regulating switch .U in case the pointer B is then above the contact z. In such case, the resultant movement of the contact 2' into engagement with the contact 11 connects the conductor 13 to the supply conductor 2 15. This short-circuits the coil U and opens the switch U if the latter were previously closed. When the thermo-couple T is connected to the meter winding b, and the temchamber temperature is perature of the thermo-couple is not high enough to hold the pointer B above the contact z', the movement of the contact it into engagement with the contact h by, the depressor and pointer, and the movement of the contact 7' into engagement with the contact j by the depressor part C are each without effect on the regulating switch U, since with the contacts Oand O separated, the contacts it and j are not connected to any source of energy except through the contacts h and 7', respectively.

The general mode of operation of the particular form of our improved electric furnace control system illustrated in the drawings,

may be summedfup as follows: The resistor Y and furnace chamber temperature measuring thermo-couples T and T, respectively, are alternately connected at regular intervals to the control instrument A, and through thelatter each thermo-couple controls the rate of supply of heat to the furnace half of the time of heat supplied to the furnace is dependent on the resistor temperature measuring thermo-couple T, the rateat which heat is suppliedis maintained at less thanthe maxi-' mum rate'if the temperature to :whichthe Duringeachiof the periods in which the rate thermo-coupl'e T responds then is equal to or exceeds a predetermined maximum. This method of controlmayserve to protect, the resistor R against dangerous overheating and may also be employed to prevent thefurnace heating up at an undesirably rapid rate.

With the described method of regulation, 4

the switch U willlae closed only half of the time during any period in which the low temperature in the furnace chamber S makes rapid heating desirable, but in which the temperature of the resistor R is so high as to make it unsafe or undesirable to supply heat at the maximumrate. Under less extreme and more usual conditions, when the furnace below the maximum desired, heat will be supplied to the furnace at themaximum rate except for occasional half minute intervals in which the thermocouple T causes the heat supply to be interrupted as required to protect the resistor R against overheating. When a portion of the heat requirements of the furnace S is supplied by a manually controlled resistor R, the latter should be-of such character as to carry full current for the period of operation required without danger of overheating.

Those skilled in the art will understand that changes in the form of the apparatus and mode of operation specifically disclosed may be made without departing from the spirit of our invention as set forth in the appended claims, and that certain features of our invention may be used without a corresponding use ofo'ther features. In particular it is to be understood that the general method of electric furnace regulation disclosed and claimed herein can be carried out by means of other control apparatus than that disclosed in Figs. 1 to 6, and that various novel features of construction and arrangement of the control instrument proper can be utilized for other purposes than as a part of the electric furnace control system disclosed and claimed herein; a

' Having now described our invention, what we claim as new and desire to secure by Letters Patent is:

'1. The method of controlling the current flow throu h an electric furnace heating resistance, which consists in making said current flow dependent on the temperature of said resistance during each of a series of regular time intervals, and during each of another series of'time intervals alternating with the intervals of the first mentioned series, making said current flow dependent on a temperature condition of said furnace dependent on, but not proportional to the temperature of said resistance.

2. The method of controlling the strength of the current flowing through an electric furnace heating resistance, which consists in exerting a current reducing effect during each of a series of regular time intervals in which the temperature of said resistance exceeds a predetermined maximum and during each of another series of time intervals alternating with the intervals of the first mentioned series, regulating said current in response to a furnace temperature condition dependent upon, but not proportional to the temperature of said resistance.

3. In a control system, a member, automatic means for subjecting said member to the control of first one and then the second of two variable quantities in regular alternation, control devices selectively actuated by said member in accordance with the value of the quantity. by which it is controlled, a regulating device, operative connections between said control devices and said regulating device, and means for automatically changing the operative connections between some but not all of said control devices and said regulating device when said member passes from the control by one of said quantities to control by the other.

4. In a control instrument, an electric meter, a time controlled switch mechanism for connecting said meter first into one and then into the other energizing circuit, control circuits including contacts selectively actuated by said meter in accordance with the degree of its energization, and means for energizing circuit into which the meter is connected is varied.

5. The combination with an electric furnace and its heating resistance, of a device responsive to the temperature of the furnace heating resistance,a device responsive to a furnace temperature normally lower than the first mentioned temperature, a meter, mechanism automatically connecting said meter alternately to said devices at regular intervals, and means controlled by said meter for supplying current to said heating resistance at rates dependent on the temperature of the device to which said meter is connected.

6. The combination with an electric res stance furnace, of a thermo-couple responsive to the temperature of the furnace heating resistance, a thermo-couple responsive to a furnace temperature normally lower than the first mentioned temperature, a meter, mechanism automatically connecting said meter alternately to the two thermo-cou les at regular intervals, and means controlle by said meter for supplying current to said heating resistance at rates dependent on said second temperature when said meter is connected to said second thermo-couple and for maintaming a rate of current supply less than the maximum when said meter is connected to the first mentioned therlno-couple and the temperature thereof exceeds a p, edetermined maximum.

7. The combination with a furnace and an electric heating resistance therefor, of a meter, meter energizing means responsive to the temperature of the heating resistance,

meter energizing means responsive to a normally lower furnace temperature, mechanism for alternately connecting one and then the other of said means to said meter, control devices selectively actuated by said meter in accordance with the temperature of the said means to which the meter is connected, a current supply regulator for said heating resistance, and operative connections between said devices and regulator including a part actuated by said mechanism tending to adjust said regulator to diminish the supply of current on the actuation of either of said devices when said meter is connected to one of said energizing means, and on the actuation of one only of said devices when the meter is connected to the other of said energizing means.

8. In a control instrument, an electric meter, an automatic switch mechanism for alternately connecting said meter into each of two energizing circuits, a plurality of control devices selectively actuated by the meter, a regulator, operative connections between said devices and regulator including means dependent onsaid mechanism for rendering the connection between one of said control devices dependent on whether said meter is connected into one or the other of said circuits. j

9. In a control instrument, an electric meter,-an automatic switch mechanism for alternately connecting said meter into each of two energizing circuits, two control devices selectively actuated by the meter, a regulator, operative connections between each of said devices and said regulator including means dependent on said mechanism for rendering the connection between one but not the other of said control devices dependent on whether said meter is connected into one or the other of said circuits.

10. Control apparatus comprising in combination an electric meter, an actuating mechanism, switch means actuated by said mechanism for alternately connecting said meter into two different energizing circuits, two control devices selectively actuated by said meter, aregulator, and operative connections between said control devices and regulator includin means controlled by said mechanism for subjecting said regulator to the control of both of said devices when the meter is con nected intoone of said circuits and subject to the control of only one of said devices when the meter is connected into the other energizing circuit.

11. Control apparatus comprising in combination an electric meter, an actuating mechamsm, switch means actuated by said mechanism for alternately connecting said meter into each of two energizing circuits, low, intermediate, and high control devices selective- 1y actuated by the meter according to the degree of its energization, a regulator, and operative connections between said regulator and control devices including means dependent on whether said meter is connected into one or the other of said energizing circuits for adjusting said regulator in one direction when said low device is actuated and in the opposite direction when either of the other devices is actuated as a result of the connection of the meter into one of said circuits, and for actuating said regulator in response to the actuation of one of said devices only when said meter is connected into the other of said circuits.

12. Control apparatus comprising in combination an electric meter, an actuating mechanism, switch means operated by said mechanism for alternately connecting said meter into each of two energizing circuits, low, intermediate, and high control devices selective ly actuated by the meter according to the degree of its energization, a regulator, and operative connections between said regulator and control devices including means dependent on whether said meter is connected into one or the other of said energizing circuits for ad- 355 said re ulator in one direction when 3 g g said low device is actuated and in the opposite direction when either of the other devices is actuated as a result of the connection of the meter into one ofsaid circuits, and for actuating said regulator in response to the actuation of said high device only when said meter is connected into the other of said circuits.

13. In a control instrument, the combination of a movable meter element, a pair of control devices adapted to be selectively actuated by said element according to the positions of said devices along the path of movement of the element, means for adjusting one of said devices along said path of movement, a connection between said devices whereby the adjustment of the one element may affect an adjustment of the second element, said connection including provisions for lost motion whereby one device may be adjusted relative to the other.

14. In a control instrument, the combination of a movable meter element, a pair of control devices adapted to be selectively actuated by said element according to the positions of said devices along the path of movement of the element, means for adjusting one of said devices along said path of movement, a in and slot connection between said devices whereby the adjustment of the one element may affect an adjustment of the second element and whereby one device may be adjusted relative to the other.

15. In a control instrument, the combination with a movable meter element pivoted to swing about an axis, a pair of cofitrolaievices adapted to be selectively actuated by said pointer and each comprising a supporting arm pivoted to turn about an axis in proximity to the first mentioned axis, a rack and pinion connection to one of said arms whereby the latter may be adjusted about its pivotal axis, and a connection between the twoarms where- -by the adjustment of said one arm permits of an adjustment of said second arm, said connection including provisions for lost motion whereby a limited relative adjustment of said arms may be affected.

lfi. In an electric metercomprising an en ergizing winding, a pointer, a depressor bar, and an actuating mechanism for intermittently actuating said depressor bar, the improvement which consists in two opposing pairs of spring contacts, including a pair of contacts one connected to one and the other to the second of the terminals of said Winding, and means actuated by said mechanism for alternately shifting-the last mention-ed contacts between two positions in one of which the last mentioned contacts respectively engage the two'spring contacts of one pair andin the other of which they respectively engage the other two spring contacts.

17. In an electric meter comprising an energlzing winding, a pointer, a depressor bar,

an oscillating switch to bee era ivel Y connected to ment of said control mechanism so that said temperatures are automatically maintained at difierent values.

Signed at Philadelphia, in the county of Philadelphia, and State of Pennsylvania,

this 13th day of July, A. D. 1925.

ROSCOE D. BEAN. FREDERICK W. SIDE.

sitions in one of which the last mentioned contacts respectively engage the spring contacts of one pair and in the other of which they respectively engage the other two spring contacts.

18. In a control system, a plurality of temperature responsive devices, a control mechanism, means for switching said control mechanism from one to another of said temperature responsive devices at regularly successive time periods, and means for simultaneously varying the adjustment of said control mechanism.

19. In a control system, a plurality of temperature responsive devices. each at a posi-' t-ion to be maintained at a temperature different from the temperatures at the other positions, control apparatus, controlling mechanism operated by said control apparatus in accordance with a temperature at one of said temperature responsive devices, means for switching said control apparatusfrom one to another of said temperature responsive devices at regularly successive time periods and means whereby said control apparatus operates said controlling mechanism to maintain the specific temperatures at each of said temperature responsive devices.

20. The method of temperature control for a furnace which consists in supplying heat to the furnace through a furnace heater at a rate which is dependent upon the temperature of p the heater durlng regularly repeated time intervals, and during other time intervals alternating with the first mentioned intervals at arate which is dependent upon the temperature at a point in the furnace at which the temperature is normallylower than the heater temperature.

21. In a temperature control system, a plurality of devices each responsive to changes in value of a corresponding one of a plurality of temperatures, a control mechanism adapted and actuated by, first one and then another of said devices and including provisions for exerting a controlling effect on the value of the particular temperature to which the device operatively connected to said mechanism responds, means for operatively connecting said control mechanism first to one and then to another of said devices at regularly successive intervals, and means for simultaneously varying the adjust- 

